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RE:




----- Original Message ----- From: "Sim Koning" <simkoning@msn.com>
To: "jrc" <jrccea@bellsouth.net>; <dinosaur@usc.edu>
Sent: Thursday, September 25, 2008 7:34 PM
Subject: RE:





Before I continue, does anyone know if a 5 ounce Archaeopteryx could carry a 1 pound coconut?


..........Probably depends largely on how well the backpack is constructed :-)


From: jrccea@bellsouth.net
To: simkoning@msn.com
CC: dinosaur@usc.edu
Subject: Re:
Date: Thu, 25 Sep 2008 04:30:00 -0600

comments inserted.
JimC

----- Original Message -----
From: "Sim Koning"
To:
Sent: Wednesday, September 24, 2008 11:54 PM

Orstriches have large wings (relatively speaking), but they have completely lost their flight feathers, which have been replaced with soft downy insulatory feathers that they also use for display.

Even so, ostriches use their wings to assist in turning while running.

If they leapt into the air, these "wings" would actually slow them down
due to drag,

Drag by definition is resistance to an object moving through fluid, which must be overcome by thrust which in turn (in the case of a wing) produces lift: so basically it would slow them down if they extended their wings.

........... As I said before, feathers can be used to modify form drag. For example, modifying an essentially circular cross-sectional shape into a shape that more closely resembles an airfoil (in cross section, not planform) can reduce drag by a factor of as much as 25. Therefore, extending arms WITHOUT feathers can have a drag penalty as much as 25 times greater than exending the same arm if it does have feathers.

This would explain why many flightless birds have completely lost their flight feathers and have extremely reduced wings.

............I tend to suspect that the driving force behind those changes is the reduced biological cost of the moult.


Why presume that the early wings make them less streamlined when jumping?

Would you race a motorcycle while wearing a cape?

...........Why use a non-applicable analogy?

I imagine it would have a similar effect If the earliest forms had simple elongated protofeathers, or even primitive flight feathers for that matter. Yes a simple wing could extend their jump, but it would also slow them down due to drag

...........Actually, once clear of the ground it can be used to speed them up even when gliding, by their conversion of potential energy back to kinetic, and by the reduction in form drag when the arms are extended.

Yes, which is possibly why the wings could be oriented to modulate or
increase traction rather than reduce it.

Why haven't flightless birds kept this feature? The only birds that do this, do it to run up trees and then jump out of them.


.........Ostriches do it.

If they leapt into the air, they would rapidly decelerate, making them unstable.

........Once in the air, the wings can be positioned to allow the animal to accelerate on its way back to the ground. Note that I'm not saying that they would use the double-diamond configuration that allows speeds over 240 mph, but they can be used to allow horizontal speeds well over that which can be achieved by running (high wingloading helps in that regard).

Since many improvements in parachuting and/or gliding ability don't lead
toward the direction of powered flight, doesn't that create problems for
your scenario?

How do you know this? If a gliding rodent begain evolving extended webbed fingers it could gradually lead to the same condition seen in bats. Sometimes the only difference between a gliding aircraft and an airplane is one has thrust, one does not; otherwise the wing design is largely the same. In fact some gliders have engines that are used occasionally. A highly efficient gliding animal could probably reach a state of sustained flight by simply using the wind; from that point it would only need to develope way of producing thrust.


............. Well, no machine or animal can extract extended flight energy from a uniform wind when no shears are present, and it takes a pretty derived wing/control system to extract energy from the chaotic processes that result in microlift (as just one example of atmospheric processes that can be used to enable flight). My point was that improvements in proto-gliding capability lead toward glding adaptations that make the powering of flapping flight more difficult. I note in passing that large soaring birds didn't develop until after the pterosaurs were gone, so apparently at least some early birds were better flappers than soarers.



How many apes seem to be developing sapience?

........ Most ?

Which jump out of water to escape predatory fish. What are these protobirds doing, jumping up to a convenient biting hight for a 10 foot tall theropod?

...........Once in the air, they would rapidly accelerate away from the big guy's reach (that high wingloading again). Even a one percent increase in escape rate would pay off over the long haul.

If they are jumping to catch prey, the immediate drop in velocity due to drag would cancel out any benefit for a cursorial predator.

..........Why not just jump higher than the prey and use the rapid acceleration due to high wing loading to overtake him in the air? Peregrine falcons have taken this to the point of passing their prey in the air, turning around upside down with extended claws, and slowing so that the prey runs right into their grasp. I can't see an early bird taking it to that extent, but it's a fascinating example of an extreme.

Which demonstrates that there is more than one way to skin a cat. A good
place to mention that the ground up vs. trees down scenario is a perfect
example of a potentially false dichotomy.

..........Have I said that before? It bears repeating. Any animal that is developing flight can access more varied sources of energy as the ability develops, whether that energy be potential, kinetic, or chemical.


JimC